1. Field of the Invention
The present invention relates, in general, to a device and method for automatically vibrating the working members of a power construction vehicle such as power excavator and, more particularly, to an automatic vibration device and method effectively used for performing an excavating, breaking or ground hardening operation of a power construction vehicle provided with a plurality of working members such as an arm, boom and bucket.
2. Description of the Prior Art
As well known to those skilled in the art, during an excavating, breaking or ground hardening operation of a power excavator, it is possible for the bucket or breaker to be overloaded. Therefore, the control levers of an excavator are manually levered by an operator during such an excavating, breaking or ground hardening operation. However, such a manual operation is inconvenient to the operators, so that it is necessary to automatically control the hydraulic system of an excavator during such an excavating, breaking or ground hardening operation. In order to achieve the above object, the following automatic vibration devices are used in the prior art. A typical automatic vibration device automatically and repeatedly reciprocates an arm, boom or bucket cylinder, which is associated with a necessary operation, and thereby automatically vibrates an associated working member such as an arm, boom or bucket. Another typical vibration device changes the amplitude of vibration of the working members in response to an electric signal generated from the control levers, thereby being somewhat convenient to an operator who levers the control levers during an excavating or ground hardening operation of an excavator. FIG. 2 shows a typical automatic vibration device for power construction vehicles, which is disclosed in Japanese Patent Publication No. Hei. 6-99948. As shown in FIG. 2, the Japanese vibration device includes a plurality of switches: an auto-vibration switch 10, a vibration mode switch 11 and a working mode switch 12. When the auto-vibration switch 10 is turned on, signals output from the two mode switches 11 and 12 are input into a controller 9. Upon receiving the signals from the mode switches 11 and 12, the controller 9 operates the signals and outputs electric control signals to a proportional control valve. The proportional control valve thus controls an associated directional control valve in response to the current control signal from the controller 9, thereby causing the directional control valve to intermittently feed pressurized fluid from a hydraulic pump to an actuator 13. For example, the Japanese automatic vibration device may automatically reciprocate the actuator 13 thereby vibrating an associated working member while bringing the relation between the amplitude (e1) of vibration in an up-motion of the actuator 13 and the amplitude (e2) of vibration in a down-motion of the actuator 13 into e1=e2. The above vibration device also may input levering signals, corresponding to levering angles of the control levers 8, into the controller 9 which operates the levering signals. After operating the levering signal, the controller 9 outputs a current control signal in order to automatically reciprocate the actuator 13 thereby vibrating the working member while changing movement of a spool in the directional control valve and bringing the relation between the two amplitudes (e1 and e2) of vibration into e1&gt;e2 or e1&lt;e2.
However, the above automatic vibration device during a vibration operation exclusively changes the amplitude of vibration of a working member in response to the levering signals from the control levers 8. Thus, it is necessary to use another select switch in order to change the number of vibrations of the working member during a vibration operation.
Another problem of the above automatic vibration device resides in that it necessarily has a select switch in order to select a working member, for example, an arm, boom or bucket, to be vibrated.